The oxidation of alkyl substituted aromatic hydrocarbons and particularly dialkyl aromatics under suitable conditions to yield the corresponding dihydroperoxides is well known. The aromatic dihydroperoxides have found use as oxidizing agents and free radical initiators for a number of polymerization processes and are valuable in preparing polyhydric phenols such as hydroquinone, resorcinol and the like. In preparing the latter products, it is well known to rearrange the dihydroperoxide percursors in the presence of acid catalyst to form the corresponding phenol and carbonyl compound.
A most efficient means for preparing dihydroperoxides such as para-diisopropylbenzene dihydroperoxide includes an oxidation reaction in which para-dialkylbenzene is oxidized in the presence of an alkaline material. In preparing the dihydroperoxides it is also the practice to continue the reaction only partially to completion, based on the total amount of dialkylbenzene present. It is found that at higher concentrations the dihydroperoxide begins to decompose resulting in a reduced yield of dihydroperoxide based upon dialkylbenzene feed. Yet, since the reaction is carried only to partial completion, large amounts of monohydroperoxide, the dihydroperoxide intermediate, as well as unreacted dialkylbenzene are present in the oxidation reaction mixture. Thereafter, as the solid dihydroperoxide product is recovered by suitable techniques, significant amounts of these precursors are retained in the solid product. Accordingly, it is desirable to separate the monohydroperoxide and dialkylbenzene from the dihydroperoxide to achieve improved quality of the latter product as well as to recover the valuable precursors for recycle to the oxidation reaction.
A number of techniques have been proposed for recovering solid dihydroperoxide free from monohydroperoxide. A common method for separating dihydroperoxides from monohydroperoxides has been to subject mixtures of these products to an aqueous alkaline solution, usually dilute sodium hydroxide, to form the sodium salts of the two hydroperoxides. The salt of the monohydroperoxide remains in the organic phase, while the salt of the dihydroperoxide dissolves in the aqueous phase. The aqueous phase is separated from the organic phase, neutralized with a weak acid and the dihydroperoxide precipitates and is recovered. One objection to such a separation technique is that additional water is added to the dihydroperoxide which must be subsequently removed. The presence of moisture is especially undesirable where the dihydroperoxide is to be rearranged as previously noted since it dilutes the acid catalyst and lowers reaction rates. Further, separation of the organic and aqueous phases and neutralization require acid consumption and additional process steps in order to recover uncontaminated dihydroperoxide in good yield.
Another method proposed for separating dialkylbenzene and monohydroperoxide from solid dihydroperoxide comprises repeatedly washing or resuspending the product with a suitable solvent and filtering the dihydroperoxide until the desired purity is achieved. It will be appreciated that such repeated washing or suspension and refiltering of the hydroperoxide product mixture with additional amounts of hydrocarbon would eventually result in successful sufficient separation of the products. However, concomitantly, the technique also results in the loss of unnecessary amounts of dihydroperoxide even by use of a hydrocarbon such as benzene in which the dihydroperoxide is only slightly soluble. Repeated washing and filtration steps are both time consuming and require expenditure of rather large amounts of hydrocarbon from which the dialkylbenzene and monohydroperoxide must be separated before recycle to the oxidation reaction.